The board of trustees of a special hospital district included wholly within a county may determine, from time to time, whether trustees shall be elected at large or from single-member districts and, if the latter, shall determine, based upon the 1990 or a subsequent federal decennial census, the boundaries of such single-member districts, which shall be contiguous, compact, as equal in population as is practicable and otherwise in compliance with applicable law. The board shall redetermine the boundaries once following every federal decennial census, beginning with the 1990 census, in accordance with the same criteria. The board may change from at large elections to single-member districts or from single-member districts to at large elections and shall determine the procedure for transition from at large to single-member districts or vice versa.